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Firefighting is a dangerous and difficult job performed in a hostile and dangerous environment. During a fire the air inside a burning structure can rapidly fill with dense smoke that can reduce visibility to only a few inches. The temperature within the structure can range from 200xc2x0 (F.) to 400xc2x0 (F.) near the floor and often be between 1000xc2x0 (F.) to 2000xc2x0 (F.) near the ceiling. Flash over, which is when the entire environment within the structure may reach 1000xc2x0 (F.) to 2000xc2x0 (F.), can cause incineration of virtually all combustible material. A firefighter who has become separated or disabled needs to be located very quickly to prevent an injury from occurring or to rescue the firefighter after an injury has occurred. If the location of the firefighter is not known an area search must be performed. The difficulty of performing an area search is compounded by the firefighters own equipment, which typically includes a helmet, air supply, coat, trousers, boots, and gloves that are designed to protect the firefighter from the surrounding hostile environment. This equipment which may weigh in the range of 50-70 lbs, makes movement difficult and restricts visibility even more. In addition, the scattering of light due to the smoke particles can severely restrict the effectiveness of flash lights.
Passive infrared imaging systems have been used to aid in location of firefighters lost or injured within a burning structure. However, these systems which distinguish objects based on the temperature difference between the object and its environment are better equipped to locate the fire itself. In addition, the system may be unable to distinguish a body from a group of burning embers in the shape of a person. Additionally, infrared light is scattered by smoke particles resulting in an image that is attenuated and blurred. Another problem for passive infrared systems is the rapidly changing temperature within the structure. As the temperature within the structure rises the victims temperature becomes lower than the surrounding area and becomes difficult to detect as the system may be saturated by the intense heat of the fire. Finally, the firefighters protective equipment is designed to minimize heat flow from the firefighter, thus making the temperature on the surface of the equipment very close to that of the environment making a fully outfitted firefighter invisible to the system.
As noted above, Rayleigh scattering scatters a wave, such as light or sound, that is passing through a medium that includes particulate matter that has a dimension that is small when compared to the wavelength of the wave. Smoke particles will scatter light, which is known as Rayleigh scattering, reducing the effective visibility within the smoke filled environment to a few feet at best. Rayleigh scattering of a wave is inversely proportional to the fourth power of the wavelength of the wave passing through the medium. Visible light has a wavelength of approximately 400-700 nanometers(nm) and will undergo greater Rayleigh scattering than infrared light having a wavelength greater than 700 nm.
Radio frequency systems using triangulation or the global positioning system (GPS) have been proposed for locating firefighters as well. In order to design a highly directional system with sufficient accuracy to locate a person within a structure, frequencies having wavelengths on the order of one inch or less would be preferred. This translates to frequencies in the range of 10 GHz or higher. However, interference caused by the materials that are contained within the buildings and that the buildings are fabricated from will be severely reflected and attenuated by the structure rendering them unsuitable for use in locating firefighters within a burning structure.
Therefore, it would be advantageous for a tracking and navigation system to be able to operate within the hostile environment of a burning structure without being affected by the smoke, heat, and the structure itself.
An apparatus and method is disclosed for locating individuals, such as firefighters, and navigating in a smoke filled environment using a beacon unit transmitting an omnidirectional ultrasonic signal that is received by a tracker unit. The tracker unit includes a directional ultrasonic transducer coupled to an ultrasonic receiver. The ultrasonic receiver provides an indicia of the signal strength of the received ultrasonic signal, thus indicating the approximate azimuth angle to the beacon unit from the tracker. The indicia can include visual indicia such as varying the intensity or pulse rate of a single light source, or providing a linear array of lights wherein the number of light sources illuminated is indicative of the received signal strength. Alternatively, an audio signal such as varying the pitch of an audio signal or varying a pulse rate of an audio signal may be used to indicate the received signal strength. The ultrasonic signal may be modulated to include encoded digital data that may be used to identify individuals, objects, dangerous conditions, or exits.
In another embodiment, the beacon unit and tracker unit can both include an ultrasonic transmitter and receiver coupled to an ultrasonic transducer. The beacon unit provides an omnidirectional ultrasonic signal and the tracker unit includes a directional receiver that provides an output indicia of the signal strength of the received ultrasonic signal. The tracker unit sends an interrogation pulse to the beacon unit that responds with an answer pulse. To avoid self-interference, the interrogation pulse and the answer pulse may be different frequencies, different pulse widths, or both. The tracker unit and beacon unit can be configured and arranged to determine the range between the tracker unit. In this embodiment, both the azimuth angle and the distance to the beacon unit from the tracker unit may be determined. The beacon unit can be configured and arranged to provide a modulated ultrasonic signal that can include encoded digital data that is received by the tracker unit and decoded to identify individuals, objects, dangerous situations, and exits. Additionally, voice modulation may be added to the transmitters of both the beacon unit and the tracker unit to provide voice communication therebetween.
In another embodiment, a plurality of directional ultrasonic transducers and corresponding ultrasonic receivers can be arranged in a one-dimensional linear array. The received signal strength from each receiver is analyzed and displayed on a linear array of light sources that indicate the azimuth angle between the beacon unit and the tracker unit. The plurality of directional ultrasonic transducers can also be arranged in a two-dimensional array, and the resulting received signal strengths analyzed to determine both the azimuth and the elevation between the beacon unit and the tracker unit.
Another embodiment includes a method to convert non-directional ultrasonic transducers into directional ultrasonic transducers by use of an acoustic horn to take advantage of commercially available devices.
Another embodiment includes a method to generate a narrow-band filter whose frequency is tunable and crystal controlled to allow the Tracker to be rapidly switched from one ultrasonic frequency to another. The bandwidth of this filter can be adjusted to be sufficiently narrow to reject interfering signals commonly found in fire scenes.
Another embodiment of this invention includes an algorithm to simplify calculation of square root of sum of squares of signal magnitudes.
Another embodiment of this invention includes a method to reduce the apparent amplitude of ultrasonic transducer sidelobes by combining a scanning technique with automatic gain control.
Another embodiment of this invention, includes a permanently mounted Tracker in a building, include methods to modify the Tracker so that it automatically senses both the presence and the direction of a Beacon.
Another embodiment of this invention includes the use of coded Beacons in exit signs to transmit evacuation instructions to evacuees.
Another embodiment of this invention includes a Tracker with an omnidirectional transducer suitable for being lowered into sections of a collapsed structure to search for fallen firefighters.
Another embodiment of this invention includes the capability of the Tracker displaying an actual image of the fire scene. In this embodiment, the Tracker is converted to a multi-pixel receiver by use of an array ultrasonic transducer and a Fresnel zone plate. Like TICs, an imaging system using this technique would be able to xe2x80x9csee through smoke.xe2x80x9d However, such a device could be considerably lower in cost than TICs. An ultrasonic imaging system of this type would have applications in detection of concealed weapon
Other embodiments of this invention include methods to combine the ultrasonic Beacon/Tracker system with other technologiesxe2x80x94particularly thermal imaging systems and video (visible optical) imaging systems. One such improvement includes adding a pulsing heat source to a Beacon so that the thermal imaging camera (TIC) can detect the Beacon. A second such embodiment involves incorporating the Tracker technology into the TIC, so that the camera can detect and display the strength of the received ultrasonic signal on the camera screen. This improvement significantly extends the TIC performance, which is normally limited to line-of-sight operation, by sensing reflected ultrasonic signals. A third embodiment combines the ultrasonic imaging version of the Tracker with both thermal and optical imaging systems for both fire scene applications as well as detection of concealed weapons.
Additional aspects, features and advantages of the present invention are also described in the following Detailed Description.